1. Field of the Invention
This invention relates to optical fibre communications networks and in particular, but not exclusively, to the provision of networks serving single line telephony out stations.
2. Description of Related Art
One approach to the deployment of an optical fibre communications network is the so called FAS network as described in the paper entitled "Future evolution of British Telecom's private circuit and circuit switched services" by Dr. S O'Hara, IEE Colloquium February 1986 which is aimed at the telephony and data needs of large business customers with ten or more lines. A principal drawback of the FAS type architecture is that it relies on direct, dedicated point-to-point optical links from each customer to the local exchange. This means that small to medium business customers with typically only two to five lines cannot be economically connected to a FAS type network. For residential customers with a requirement for single line telephony the cost requirements are still more severe and it appears from present estimates that it is unlikely that a direct optical connection per customer from the exchange will ever be a commercial possibility.
One proposal for extending the use of optics beyond large business customers, is to provide new broadband services in addition to the telephony service, such as cable television for example, as described in "The British Telecom switched star network for CATV" by W. K. Ritchie, BT Technology Journal, Sept. 1984.
In such an approach the strategic aim is to seek to move towards an integrated multiservice network, conveying both narrowband services (telephony+data) as well as broadband (entertainment TV, video library service etc) so that the relatively high cost of extending an optical connection to the residential customer can be justified by the combined revenue of both types of service. The major difficulty with this approach, however is that there is not yet an adequate customer demand for such services to justify the very substantial investment that would be required. The view is nevertheless widely held both in the UK and abroad that the eventual development of integrated multiservice networks is inevitable and will most likely occur at some stage during the 1990's. While such circumstances continue to prevail, any further extension of optical technology into the local loop must be largely justified on the basis of providing cost effective solutions for the provision of the basic telephony/data services.
One possible approach is a partial optical solution in which the optical network extends only as far as the street distribution point (DP), with the known copper wire link being used for the final feed to the telephony/data customers.
There are several disadvantages with this approach. It requires the use of remotely stationed electronics in the field in concentrating traffic economically onto highly multiplexed feeders back to the exchange. Active electronics is in general required both at the street Cabinet level and the DP. The latter is also street located except for business customers large enough to justify their own DP. For such a system there are potential problems related to the maintenance, reliability, power feeding and power consumption of the remote electronic nodes.